1. Technical Field
The present invention relates to a communication apparatus, a communication method, and an integrated circuit capable of carrying out communication using a plurality of subcarriers.
2. Background Art
A transmission scheme of using a plurality of subcarriers, such as an OFDM (Orthogonal Frequency Division Multiplexing) scheme has a big advantage of realizing high quality communication even over a transmission channel of a severe condition, and thus is used for wired communication such is as power line communication as well as wireless communication. A frequency band usable for the power line communication is generally in the range of 2 MHz to 30 MHz as in JP-A-2007-259176. The frequency bands usable for the power line communication are each assigned as a proper value of each nation according to the national law of each nation. However, it is considered that a broader frequency band containing a higher frequency is used.
As for the transmission of the OFDM scheme, a communication speed (communication rate) in the broad frequency band is improved theoretically, but the communication rate is not always improved actually. That is, attenuation generally increases as a frequency band is higher and the output in the high frequency band is relatively restrictive in the power line communication in consideration of an influence on other electrical devices (depending on nations, the output needs to be lowered by 27 dB or more in the power line communication using a frequency up to 80 MHz, compared to the power line communication using a frequency of 30 MHz or less). In addition, under such an environment, a level difference between a spectrum of a low band (for example, 30 MHz or less) and a spectrum of a high band (for example, 30 MHz to 80 MHz) is inclined to increase when the power line communication apparatus of a broadband expanded up to 80 MHz is realized. Accordingly, since a wide dynamic range is necessary for an AD converter or a DA converter, it is not easy to realize a power line communication apparatus capable of carrying out communication in a state where the low band and the high band is both used optimally. Moreover, since variation in the state of the power line depends on the frequency band, the power line communication of the broadband does not necessarily become a communication scheme of the highest rate.
A frequency spectrum illustrated in FIG. 17 is a spectrum for the power line communication used for a frequency band in the range of 2 MHz to 80 MHz. There is a level difference LD of an output between a spectrum SL at a low frequency band (2 MHz to 30 MHz) and a spectrum SH at a high frequency band (30 MHz to 80 MHz). The level difference LD between the low band spectrum and the high band spectrum generally increase when a TDM (Time Division Multiplex) is carried out using the low band and the high band simultaneously. Therefore, a dynamic range DR is necessary for the AD converter and the DA converter.
When a FDM (Frequency Division Multiplex) is carried out using the low band and the high band, a perspective problem (which refers to a phenomenon that the level difference is considerable between the low band and the high band) of the low band and the high band occurs in addition to the restriction of the TDM, thereby requiring the wider dynamic range. Moreover, in order to narrow the dynamic range in the FDM, a steep BPF (Band Pass Filter) is necessary. However, it is generally difficult to use the steep BPF. Therefore, when the FDM is carried out using the low band and the high band, it is necessary to determine a communication scheme in consideration of signal leakage in a frequency band of an opponent side.
Such a circumstance is not limited to the power line communication carrying out communication with the power line as a transmission channel, but the same is applied to multicarrier communication carrying out communication with another wired transmission channel or multicarrier communication carrying out communication with a wireless LAN.